What is the difference between a rat and a mouse?

There are just three species of rat and mouse that are by far the most prevalent and important pests in homes and businesses worldwide due to their ability to adapt to the human environment.

It is essential to control them as they are major pests of homes and businesses handling food and they can spread a large number of diseases.

The three species are:

• Brown rat (Rattus norvegicus): also called the common or Norway rat
• Black rat (Rattus rattus): also called the ship rat or roof rat. It is not common now in temperate countries and is mainly confined to buildings near ship ports
• House mouse (Mus domesticus): the house mouse has several subspecies that are common in different parts of the world and are increasingly being recognised as separate species, but these are all virtually indistinguishable from each other

All rodents have the common identifying feature of a pair of incisor teeth in the upper jaw. Their other characteristics and behaviours are different, however, and give us a number of options for identifying them. Here are six features that show the differences between rats and mice:

Physical appearance

Rats and mice to the inexperienced eye have similar body shape, legs, tail, nose and ears, but a closer look at their body characteristics shows that there are differences in their sizes and features that you can use to distinguish these pests.

What do mice look like?

• Physical appearance
• Eating habits
• Where do rats and mice live
• Footprints and trails
• Droppings
• Breeding behaviour

• Slender body
• Weigh up to 25gm
• Length 30-100mm body + same length tail
• Large ears
• Mice are usually light grey or brown in colour with a lighter shade on their bellies
• A mouse can be confused with a young brown rat, but the mouse has larger ears and longer tail compared to its body length than the rat

What do rats look like?

The brown rat is larger than the ship rat and they have the following different body features:

Brown rat

• Thick-set body
• Adults weigh up to 500gm
• Adult length is up to 220mm body + 170 mm tail
• Tail shorter than length of head + body
• Paler colour underneath the tail
• Small hairy ears
• Blunt nose
• A young rat has distinctly larger feet and head compared to the body than a mouse .

Black rat

• Slender body
• Adult weight up to 300 gm
• Adult length up to 200mm body + 220m tail
• Tail longer than head +body
• Large thin ears
• Pointed nose.

Rat and mouse eating habits

Both rats and mice are omnivorous, but the brown rat and house mouse prefer cereals, while the black rat prefers fruit and foods with high moisture content.

Brown rat

• Prefers cereals
• Cuts grain when eating, giving the appearance that is has been chopped
• Drinks about 60ml water a day
• Tends to seek food in the same places, making baiting easier
• Brown rats show neophobia — a fear or avoidance of new foods or changes to their environment. This means they are slow to take new bait or accept new objects such as traps.

Black rat

• Prefers moist fruit
• Cuts grain when eating, giving the appearance that is has been chopped
• Drinks about 30ml water a day
• Tends not to eat at the same location on consecutive nights. This makes them more difficult to control, requiring many small baiting points using moist food, which only remains edible for a few days before needing replacing
• Shows neophobia, a fear or avoidance of new foods or changes to their environment. This means they are slow to take new bait or accept new objects such as traps.

Mouse

• Prefers cereals
• When eating it ‘kibbles’ the grain by removing the outer husk to eat the white endosperm inside
• Tends to seek food in the same places
• Doesn’t need to drink water but will drink about 3ml a day if available
• Mice are inquisitive and readily accept new food, often in preference to old ones
• Mice will visit multiple food sources a night if available, and if only one source is available will visit it around 200 times a night, eating only about 20mg each time.

Where do rats and mice live?

Brown rat

Brown rats usually live on the ground, making burrows in soil, especially near water in more open areas or next to solid objects and structures. They are frequently found in sewers, where their burrowing can cause extensive damage. In buildings their nests have been found in lofts, attics and cavity walls, where they shred available material for making their nests.

Black rat

Black rats are now mainly restricted to buildings around ports and in ships (hence the name ‘ship rat’). They are agile and good climbers, nesting high up under roofs. In tropical Asia, where they originate, black rats nest in trees, especially in woodland and orchards.

House mouse

Mice usually live on the ground and nest in burrows when outdoors. Indoors they will make nests in almost any place that is undisturbed, such as furniture, boxes, under floorboards, in attics. They will shred material such as paper to use for nesting material. They are agile and can climb to search for places to shelter.

Rat and mouse footprints and marks

Mouse

A mouse obviously has a smaller footprint than a rat. In heavy mouse infestations, grease from the body combined with dirt and urine can build into small pillars. These can remain for a long time, so may not indicate a current infestation. See the Signs of a mice infestation page for more details.

Droppings

The droppings of the three types of rodent differ in size and shape, according to the body size. Rat droppings are often mistaken for mouse droppings, but are much larger. Below are images of droppings shown next to a UK 5 pence coin (18mm diam).

Brown rat droppings

Brown rat droppings are up to 20mm in length and typically a tapered, spindle shape – resembling a large grain of rice.

Black rat droppings

Black rat droppings are up to 15mm long. They are sausage shaped, a little smaller than brown rat droppings. Black rat droppings are more regular in form with a banana like curve and pointed ends.

Mouse droppings

Mouse droppings are 3-8mm in length, and are often found scattered randomly during an infestation. The droppings are granular in shape, black and are found near nesting areas.

Breeding

Mice reach sexual maturity earlier and produce larger litters at a more frequent rate than rats. The newborne of all three rodents are blind, hairless and completely dependent on the mother for feeding and protection.

Brown rat

• Litter size: 7-8
• Number of litters per year: 3-6
• Time to maturity: 10-12 weeks

Black rat

• Litter size: 5-10
• Number of litters per year: 3-6
• Time to maturity: 7-8 weeks

House mouse

• Litter size: 4-16
• Number of litters per year: 7-8
• Maturity: 8-12 weeks